Modules 1-3 midterm

What is homeostasis?

the ability of a cell or organism to regulate and maintain its internal environment regardless of the influences of the external environment

What is a set point?

the range or point at which a variable physiological state tends to stabilize.

What are the components that make up most physiological control systems? What are their responsibilities?

• sensor

  • responsible for detecting an environmental variable

• integrator

  • compares the variable detected to the set point

• Effector

  • initiates the changes to restore the variable back to the set point

What are the two types of homeostatic regulation?

intrinsic regulation (AKA local regulation or autoregulation)

extrinsic regulation

Where are the sensor, integrator, and effector located in intrinsic regulation?

They are all located within a tissue, so that the tissue can regulate its own internal environment

Where are the sensor, integrator, and effector located in extrinsic regulation?

the regulatory mechanisms are outside the tissue.

What are the two different kinds of feedback loops?

• negative feedback

• positive feedback

What kind of response does a negative feedback loop initiate?

a response in the opposite direction as the change in the parameter

What are the steps in blood glucose regulation through a negative feedback loop?

imbalance - after eating, blood glucose rises

Response - insulin is released by the pancreas in response to high blood glucose levels

Effect - on tissues: insulin increases the ability of body cells to uptake glucose from the blood. - on liver: increases the livers ability to convert glucose and store it as glycogen

What kind of response does a positive feedback loop initiate?

a change that amplifies the initial signal

What are the steps in which a positive feedback loop is used in childbirth?

brain stimulates the pituitary gland to secrete oxytocin

oxytocin is carried in the bloodstream to the uterus

oxytocin stimulates uterine contractions, pushing the baby towards the cervix

the babies head pushes against the cervix

the nerve impulses from the cervix are transmitted to the brain, stimulating the pituitary gland again.

What are the 3 primary functions of a plasma membrane?

• ensure cell survival

• maintain homeostasis

• function cooperatively with surrounding cells

what are the 3 means by which cells are adhered together?

• ECM

• cell adhesion molecules (CAMs)

• Cell junctions

What is the ECM composed of?

a network of fibrous proteins embedded in a gel-like mixture of complex carbs.

What are the 3 major protein fibres found in the ECM, and what are their roles?

• Collagen - forms the cable-like fibres that give the ECM tensile strength

• Elastin - rubber-like protein that allows tissues to stretch and recoil

• Fibronectin - promotes cell adhesion

What is a cell adhesion molecule?

usually intracellular proteins, involved in protein - protein interactions

*help cells stick to each other and their surroundings

List the 3 types of cell junctions (name only)

• desmosomes

• tight junctions

• gap junctions

What are desmosomes used for?

used to anchor together two adjacent cells that are not otherwise in direct contact

What are desmosomes composed of?

thick plaques connected by glycoprotein filaments to attach neighbouring plaques together.

What is a tight junction used for?

to create a very tight seal between cells, preventing movement of molecules from cell to cell.

What is a tight junction made up of?

long strings of junctional proteins in the plasma membrane. neighbouring cells align and adhere these to form a tight junction

What is a kiss site?

where junctional proteins of neighbouring cells meet

Where are tight junctions primarily found? why?

epithelial tissues - allows for highly selective barriers to form between different parts of the body.

What is a gap junction used for?

direct communication between neighbouring cells

What is a gap junction composed of?

6 connexin protein subunits from one cells plasma membrane align with 6 connexin protein subunits from an adjacent cell

where are gap junctions commonly found? why?

commonly found in cardiac and smooth muscle tissue - they rely on these junctions to spread the excitation wave and secondary messengers

How does a molecules size affect its permeability?

small substances can pass through channels, whereas larger molecules need a transport protein

How does a molecules charge affect its permeability?

uncharged molecules can readily cross the plasma membrane, whereas charged molecules can’t pass through without aid

what are the 2 primary methods of passive transport?

• diffusion

• facilitated diffusion

What are the 2 primary types of active transport?

• carrier mediated

• Vesicular transport

what is an aquaporin?

channels that allow water molecules to pass

What 2 forces underlie the movement of water across a membrane?

osmotic and hydrostatic pressures

What is osmotic force?

underlying force that moves water down its concentration gradient. the greater the gradient, the greater the osmotic pressure

What is hydrostatic pressure?

force created by a given volume of water. The grater the volume the more hydrostatic pressure

What are the 3 important characteristics that determine what will be transported across the membrane in carrier mediated transport? list and briefly explain

1. specificity - each carrier protein is specialized to recognize and transport a specific substance

2. Saturation - for a given cell, there are only so any of each type of carrier protein in the plasma membrane. because of this, there is a transport maximum, or Tm (max amount of substance that can be transported at any given time)

3. Competition - sometimes several related substances can be recognized by the same carrier protein. this creates a competition and inability for either substance to reach its Tm while competing.

What are the 3 classifications of endocytosis? list and briefly explain

• pinocytosis

  • engulfs a small droplet of extracellular fluid - nonspecific

• Receptor-mediated endocytosis

  • the trigger to create the vesicle is dependent upon the binding of a substance to a specific receptor on the cell surface

• Phagocytosis

  • internalization of large multimolecular particles - only certain cell types perform it

What are the steps to exocytosis?

1. secretory vesicle formation - recognition markers in the membrane of the Golgi sac capture the appropriate cargo from the Golgi lumen by binding only with the sorting signals of the protein molecules to be secreted. a bud is formed

2. Budding from Golgi - membrane closes beneath the bud, pinching off the secretory vesicle

3. Uncoating - vesicle loses its coating and exposes v-SNARE docking markers on the vesicle surface

4. Docking at plasma membrane - v-SNARE bind only with t-SNARE docking markers to ensure that the vesicles are emptied to the exterior of the cell

5. exocytosis

What is the equation for Ohm’s law?

V = IR

What is an ion channel?

large, transmembrane protein that opens to allow ions to enter or exit cells, usually down their concentration gradient.

What are the 4 main classes of ion channels?

• voltage gated

• chemically gated

• mechanically gated

• thermally gated

What do voltage gated ion channels respond to?

they open and close in response to changes in membrane potential

What are the different conformations of voltage-gated ion channels?

1. closed at resting potential - activation gate keeps it closed

2. open in response to nerve impulse - activation gate rapidly opens

3. Inactive for a brief period following activation - inactivation gate moves to block the inside of the pore

What do chemically gated ion channels respond to?

a specific chemical messenger (ligand) interacts with it

What do mechanically gated ion channels respond to?

mechanical deformations such as stretch

what do thermally gated ion channels respond to?

changes in temperature

What is the Nernst equation for calculating the equilibrium potential?

E = equilibrium potential in mV

z = valence (or charge) of the ion

C = concentration in mM

What does the E value in Nernst equation determine?

for any given voltage, if the net driving forces move ions into or out of the cell.

What are potassiums normal intracellular and extracellular concentrations?

intra: 150 mM

extra: 5 mM

What direction will the net flow of ions always be in if the membrane potential isn’t at the equilibrium potential?

towards the equilibrium potential

What is a resting membrane potential?

the electrical potential across its membrane

What is a RMP dependent of?

• types of ion channels in a membrane

• concentration of ions on both sides of the membrane

• permeability of said ions at that time

What is the Goldman equation used to calulate the RMP?

what are the 3 different ways in which membrane potential changes and what do they mean?

• Depolarization

  • the magnitude of the polarization decreases, moves towards 0 mV

• Repolarization

  • once the polarization starts to return towards the RMP

• Hyperpolarization

  • magnitude of the polarization increases (more negative)

What are graded potentials?

local changes in membrane potential that are used for short distance signalling

what does the magnitude and duration of a graded potential depend on?

the strength and duration of the triggering stimulus

True or False: Graded potentials, once established, move far along the membrane, having a long lasting presence

False - Graded potentials lose current as they progress

Are action potentials used for long or short distance signalling? Why?

long distance - because it is propagated throughout the entire membrane and does not diminish in strength

Are graded potentials used for long or short distance signalling? Why?

Short distance - as they progress through the membrane they lose current

What does it mean when people say action potentials are “all or none”?

the triggering event to initiate the action potential has to be strong enough. It’s either strong enough and triggers and action potential, or it isn’t and nothing happens. It’s black and White

What are the 3 steps of an action potential? Explain

1. At rest

   • Majority of the voltage-gated Na and K channels are closed but they’re capable of opening

   • Incoming graded potentials can if strong enough, depolarize the membrane potential to the threshold

2. Threshold and rising phase

   • when a triggering event reaches the threshold, voltage gated Na channels open. Na permeability dramatically increases

   • membrane potential rapidly approaches the Na equilibrium potential

   *K+ voltage gated ion channels are open but their contribution is minimal

3. Falling phase

   • Voltage gates Na+ channels inactivate. This decreases Na+ permeability.

   • Because voltage gated K+ channels are still open, the membrane potential moves towards the K+ equilibrium potential.

Membrane potential is restored

What is a “refractory period”?

a period in which, even if a trigger reached a threshold, an action potential would not occur.

What does the Na-K-ATPase pump do?

removes Na from the cell and brings in K to help restore concentration gradients.

What are the 4 functional zones of a neuron? What part of the neuron do they contain?

1. input zone

   • part where the incoming signals are recieved

   • contains dendrites and cell body

2. Trigger zone

   • part where action potentials are initiated

   • contains axon hillock

3. Conducting zone

   • Part where action potentials are conducted to their target locations

   • contains the axon

4. output zone

   • part that releases chemical messengers

   • contains axon terminals

What is a dendrite?

a projection from the cell body of a neuron that recieves electrical and chemical inputs

What is cell body?

location of nucleus and other organelles in a neuron

what is an axon hillock?

part of a neuron where the axon leaves the cell body

what is an axon?

a tubular extension on the neuron that conducts the action potential away from the cell body

What is an axon terminal?

extensions of a neurons axon that releases chemical messengers

how is an action potential conducted from the axon hillock to the axon terminal?

it’s not just one action potential being transmitted down the entire axon. An action potential triggers a new action potential in an adjacent area

How does an axon ensure unidirectional propagation of the action potential?

use of the refractory periods - when the next action potential is triggered, the previous one is still finishing and the Na+ channels are still inactive

What is the difference between an absolute refractory period and a relative one?

absolute - under no circumstances can another action potential be triggered

relative - it’s difficult but if the stimulus is strong enough then an action potential can be triggered

What can increase the frequency of action potentials?

A strong signal

What are the 2 types of cells that form myelin?

oligodendrocytes and schwann cells

are oligodendrocytes associated with the CNS or PNS?

CNS

are schwann cells associated with the CNS or PNS?

PNS

What is a node of ranvier?

a region of exposed neuronal fibre - not myelinated

Where can action potentials be triggered in myelinated fibres? why?

at the nodes of ranvier - fibre is exposed to extracellular fluid. Na+ channels are densest there.

What does the term saltatory conduction refer to?

how in myelinated fibres, the wave of excitation jumps from one node of ranvier to the next

What is the relationship between neuronal fibre diameter, and conduction speed?

up to a certain size, a greater diameter means a greater conduction speed.

• the resistance to propagating local currents decreases, allowing a faster conduction

What is a synapse?

a neuron-to-neuron junction

are synaptic transmissions electrical or chemical?

chemical

What is a neurotransmitter

chemicals released into the synaptic cleft. they activate ion channels in the post-synaptic membrane

What are the steps in synaptic transmission?

1. when an action potential reaches the axon terminal in the pre-synaptic neuron, voltage gated Ca channels are open, and calcium flows down its concentration gradient into the cell.

2. calcium flows into the axon terminal, which triggers exocytosis of synaptic vesicles that contain neurotransmitters

3. Neurotransmitters diffuse across the synaptic cleft, and interact with receptors on the post-synaptic neuron. This binding opens chemically gated ion channels which modulate the postsynaptic membrane potential

what are the 2 types of postsynaptic potentials?

• Excitatory postsynaptic potential

• Inhibitory postsynaptic potential

What happens when an excitatory synapses receptors interact with a neurotransmitter?

nonselective cation channels open → movement of both Na+ and K+ occur → slight depolarization

What characterizes an excitatory postsynaptic potential?

the graded depolarization brings the membrane potential closer to its threshold

What happens when an inhibitory synapses receptors interact with a neurotransmitter?

either Cl- or K+ channels are activated → both would cause the inside of the cell to be more negative (K+ flowing out or Cl- flowing in) → moves membrane potential away from threshold

what characterizes an inhibitory postsynaptic potential?

moves the membrane potential away from the threshold

what does the term “summation” refer to? (context: nerves and synaptic transmission)

unless at rest, the axon hillock’s membrane potential will be the summation of all arriving, or recently arrived graded potentials

What are the 2 types of summation that can occur at an axon hillock? Explain

• Temporal summation

  • summing of several ESPs that happen close together in time due to the repetitive firing of a single presynaptic neuron. They each have an additive effect before the membrane returns to the resting membrane potential

• Spatial summation

  • summation of ESPs and ISPs that originate from several different presynaptic inputs to have a simultaneous effect

what are the two main components of the nervous system?

• Central nervous system (CNS)

• Peripheral nervous system (PNS)

What does the CNS consist of?

brain and spinal chord

What does the PNS consist of?

Nerve fibres that carry info between the CNS ans the rest of the body

List at least 3 complex functions that neurons within the CNS perform/regulate

• subconscious neuronal regulation of your internal environment

• Emotions

• Voluntary movement

• Perception

• Higher cognitive functions (memory and learning)

What is the afferent division of the PNS responsible for?

carrying sensory info from the periphery to the CNS where it is processed

What is the efferent division of the CNS responsible for?

send necessary instructions from the CNS to the PNS

What are the 3 functional classifications of neuronal cells? (names only)

• Afferent neurons

• Interneurons

• Efferent neurons

What is different about the cell structure of an afferent neuron?

• Has a sensory receptor at the peripheral ending

• Cell body sticks out, not in line with the axon

Where are afferent neurons mostly found?

within the PNS

Where are interneurons found?

completely within the CNS